1. Field of the Invention
The present invention relates to a biological treatment and filtration system equipment for raw water, especially a water to be treated before a drinking water is called a raw water which should be treated to absorb arsenic components and other harmful materials to the human body from raw water.
2. Discussion of the Related Art
As the typical method for preparing a drinking water from raw water, there are generally known a slow filtration method and a rapid filtration method. The former method comprises biological treatment and filtration by sand layers carrying microorganism. The inventors developed the former method and made a new method comprising a filtration by means of very minute sintered sands. The new method is useful in making no drug smell water for drink although a processing speed is not fast [Japanese patent publications tokkaihei 07-308518 and Japanese Patent No. 3406258]
The raw water usually contains impurity and harmful materials before a purify process, so that the harmful materials are filtrated through a filter having a physical small net, but it is difficult to delete arsenic components. The arsenic components exist in a soil in form of variable shapes, so that the raw water containing the arsenic component is sometimes harmful to humans. Therefore, it is recommendable to delete the arsenic components from the drinking water as much as possible.
According to the standard of drinking water, it is requested to lower the content of arsenic to less than 0.01 mg/l. There have been proposed conventional methods for absorbing or cohesively depositing the arsenic components (Japanese Publication 2007-505736 and Japanese Patent No. 3546794).